1. Field of the Invention
The present invention relates to the conveyance, storage and disposal of stormwater runoff, and more particularly concerns chambers which facilitate the infiltration of water into underlying substrate and minimize sediment maintenance requirements.
2. Description of the Prior Art
Culverts, catch basins, storm sewers and out falls are the common practices for handling, conveying and storing stormwater run-off. In some instances such water is discharged directly into the nearest available water body despite the potentially adverse environmental effects of such action. In some other instances, retention or detention basins/ponds are constructed to retain/detain the run-off. Retention and detention basins/ponds represent the most common structural approach to stormwater management. Although more environmentally sound then direct discharge into an existing water body, such stormwater management approaches preclude other uses of the land. This is of particular importance where land values are high and/or space is limited. The open ponds may also be undesirable in locations near airports because of birds attracted by the pond, or in locations where health, liability or aesthetic considerations make them undesirable. Even the use of xe2x80x9cdryxe2x80x9d detention basins frequently results in the same types of problems associated with wet ponds. Without proper maintenance, dry detention basins frequently transform into wet ponds.
Underground systems have also been developed for the storage and disposal of stormwater and/or sewage system effluent. Those systems most commonly used specifically for stormwater include large diameter pipe with a partial closing at the end to retard flow for sediment deposition; infiltration trenches, which are basically excavations filled with stone; and sand filtersxe2x80x94typically large, partitioned concrete xe2x80x9cboxesxe2x80x9d with an initial compartment for sediment deposition and a following compartment with sand and under-drains for stormwater filtration. Those commonly used for either stormwater or sewage system effluent are limited to plastic, arch-shaped, open bottom, xe2x80x9cinfiltrationxe2x80x9d chambers, the basis of the present invention. Although in limited use for approximately 10 years, the use of plastic stormwater chambers for this purpose is a relatively novel approach. Plastic stormwater chambers are also highly preferable to other types of stormwater management systems for other reasons: they are less expensive than other types of underground stormwater management devices; they are more maintenance xe2x80x9cfriendlyxe2x80x9d; longer lived; and unlike some other types of underground stormwater management facilities, can be located under paved areas. However, all current underground stormwater management systems are limited by the amount of area available for their installation.
In a typical installation, elongated hollow plastic chambers are emplaced in the ground to form a leaching field for receiving such waters and dispensing them into the surrounding earth. Such chambers have a central cavity for receiving inflow water. An open bottom, and apertures in the sides of the chamber provide the means whereby the water is allowed to exit the central cavity and disperse into the surrounding earth. The chambers are usually attached endwise to form long rows which may extend in side-by-side juxtaposition. For stormwater applications, the assemblage of chambers is generally engulfed in coarse backfill such as gravel or rock and overlying compacted soil to the surface or to a paved cover surface. The resultant installation may be used as a parking lot, roadway, sports field or for other uses.
In order to sustain the considerable downward forces imposed by the surrounding backfill and overhead vehicular traffic, the chambers are generally of arch-shaped configuration having a corrugated construction. The corrugations consist of a continuous sequence of ridges or peaks separated by valleys. The peaks and valleys are connected by web portions disposed in planes substantially orthogonal to the axis of elongation of the chamber.
Examples of such leaching chambers wherein the apertures in the sidewall are horizontal slots disposed in the peak and valley portions of the corrugations are disclosed in U.S. Pat. Nos. 5,017,041; 5,156,488; 5,336,017; 5,401,116; 5,441,363 and 5,556,231. Such leaching chambers generally have a geometrical configuration which permits nesting, thereby facilitating shipping and storage.
U.S. Pat. No. 5,511,903 discloses a corrugated leaching chamber wherein horizontal slot apertures are disposed not only in the peak and valley portions, but also in the web portions. Although a high total aperture area in the chamber sidewall facilitates the exit of water, it may also produce an undesired reduction in the strength of the chambers with respect to crushing.
New Federal stormwater regulations require state and local governments to lessen the pollutant levels in waterways, tributaries, lakes and ponds. As a result of these regulations, states and municipalities have to address ways to improve the quality of stormwater discharges. Some states and municipalities have recently completed, are in the process of completing, or plan to complete, revised Stormwater Manuals to satisfy this need. The primary targeted pollutants are sediment and nutrients (predominantly phosphorous and nitrogen).
Studies on stormwater effluent have documented that stormwater management facilities that infiltrate stormwater into the surrounding earth provide for the highest level of stormwater quality enhancement than any other type of stormwater management practice. This becomes evident when considering that a stormwater chamber system simply functions as a septic drain field for stormwater. A biomat of various microbial organisms forms on the stone and soil beneath the open bottom chambers that metabolize pollutants carried by the stormwater. The pollutants that escape metabolism within the biomat are subject to metabolism by similar microorganisms as the stormwater moves downward through the soil profile, as well as filtration through the soil column. The sediment is deposited and some is filtered out through the soil column.
Stormwater may carry considerable amounts of suspended particulate material, commonly referred to as Total Suspended Solids (TSS), which eventually settles out as sediment. The accumulation of such sediment adversely affects the storage capacity of stormwater management facilities, decreasing their effective life. The effective life of such facilities can be extended with a maintenance program for sediment removal. Unfortunately, the maintenance program utilized for most such facilities is commonly referred to as xe2x80x9cbenign neglectxe2x80x9d. This problem has become so serious that some municipalities have recently imposed a stormwater maintenance xe2x80x9cfeexe2x80x9d on all property owners to help pay for private-sector stormwater facility maintenance. The xe2x80x9cfeexe2x80x9d has not been sufficient in some cases to provide this type of maintenance for all such facilities.
The accumulation of sediment is of particular concern with underground stormwater management facilities, including stormwater chamber systems. Unlike stormwater wet and dry ponds (the most commonly used types of stormwater management facilities), by the very nature of their design, sediment management of underground stormwater management facilities has historically been inherently more inconvenient and costly. Some types of underground stormwater management facilities have to be replaced in order to remove accumulated sediment. It is therefore preferable to have a stormwater chamber system that minimizes the accumulation of sediment within the chambers and that allows for more convenient and cost-effective sediment maintenance.
The addition of excessive nutrients, particularly phosphorous and nitrogen, into receiving bodies of water accelerates their aging, adversely effects aquatic habitats, depletes oxygen, causes excessive growth of aquatic plants, causes fish kills, etc. High concentrations of phosphorous and nitrogen commonly exist in stormwater runoff, particularly in urbanized and agricultural areas. Most of the nutrients in urbanized areas come from pet wastes and fertilization of lawns and gardens. In agricultural areas, principally from animal wastes and fertilizers applied to crops. Sediment maintenance is also the key to nutrient reduction from stormwater runoff. Most of the phosphorous and nitrogen (as well as many other pollutants) are found in stormwater as part of the sediment load.
The other major concern with infiltrative stormwater management facilities, including stormwater chambers, is their effectiveness in soils with limited infiltration capability. Most municipalities will not allow the use of infiltrative stormwater management facilities on sites with soils of limited infiltrative capacity. This can be accommodated utilizing layers of sand and gravel under the chambers, underlain with perforated drainage pipe, but this solution gets expensive.
The phenomenon of the settling of suspended sediment is time and velocity dependent. The faster a unit volume of water flows, the greater its carrying capacity of total suspended solids. Conversely, total suspended solids are deposited proportionally to the decrease in velocity of flow. This is clearly seen in rivers and streams where sediment is noticeably deposited along the inner bank of curves where the velocity of flow is significantly less than the corresponding outer bank. Similarly, when a stream of water changes its direction of flow, its velocity decreases, depositing sediment. The more pronounced the change in direction of flow, the more pronounced the deposition of sediment at that location.
In leaching chambers, the velocity of axial flow is greater than the velocity of transverse flow directed through apertures in the sidewall. Accordingly, suspended particles which are caused to said move transversely with respect to the flow axis in order to exit said apertures are induced to settle out within the chamber. Such action is undesirable. It is preferable to cause the suspended matter in the water to deposit in the region exterior to the chamber.
It is a primary object of the present invention to provide a stormwater dispensing chamber which accumulates reduced amounts of sediment derived from said stormwater.
It is a further object of this invention to provide a dispensing chamber as in the foregoing object which is nestable with other identical chambers.
It is another object of the present invention to provide a dispensing chamber of the aforesaid nature having apertures which do not significantly diminish the strength of the chamber.
It is a still further object of this invention to provide a dispensing chamber of the aforesaid nature which facilitates end-to-end joinder of said chambers.
It is yet another object of the present invention to provide a dispensing chamber of the aforesaid nature which is of monolithic construction amenable to low cost manufacture.
It is another object of the present invention to provide a dispensing chamber of the aforesaid nature which provides better predictability of sedimentation concentration within the chamber.
It is another object of the present invention to provide a dispensing chamber of the aforesaid nature which facilitates sediment removal.
It is another object of the present invention to provide a dispensing chamber of the aforesaid nature which provides better predictability of a sediment maintenance schedule.
It is another object of the present invention to provide a dispensing chamber of the aforesaid nature which facilitates the use of additional pollutant removal materials.
It is another object of the present invention to provide a dispensing chamber of the aforesaid nature having integral features that help restrict axial deformation.
It is another object of the present invention to provide a dispensing chamber of the aforesaid nature with integral features that facilitate their use in lieu of a header/manifold pipe for dispersion of aforementioned stormwater into the rows of a stormwater chamber system.
It is another object of the present invention to provide a dispensing chamber of the aforesaid nature which would provide enhanced water quality capabilities on sites that do not infiltrate well.
These objects and other objects and advantages of the invention will be apparent from the following description.
The above and other beneficial objects and advantages are accomplished in accordance with the present invention by an improved water dispensing chamber fabricated as a monolithic plastic structure elongated upon a straight axis between open inlet and exit extremities and having a wall of arch shape cross section defining an open bottom and having a multiplicity of alternating peaks and valleys running along the arch shape in planes orthogonal to said axis, and intervening portions which connect adjacent peaks and valleys, said intervening portions comprising facing upstream and downstream web panels embracing each valley wherein said upstream web panel is closer to said inlet extremity than the associated downstream web panel. In the improved dispensing chamber of this invention, the upstream web panels are provided with apertures which are preferably elongated in the direction of the arch shaped path of the web panel, and the downstream web panel is integral with the corresponding valley to form a curved impingement surface which serves to deflect outwardly from said chamber water emergent from said associated apertures.